A passive optical network (PON) technology is to configure a high-speed subscriber network and configured to process simultaneous access of a plurality of subscribers through a time division scheme or a wavelength division scheme. Among the schemes, a cost-effective time division scheme is mainly used, and Ethernet PON (EPON) according to Institute of electrical and electronics engineers (IEEE) 802.3av/ah or gigabit PON (GPON) according to international telecommunication union-telecommunication standardization sector (ITUT) G.984/7 is representative.
In the configuration of such a PON, basically, a single optical line terminal (OLT) installed in a telephone station and a plurality of optical network terminals (ONTs) or optical network units (ONUs) have a point to multipoint network structure through a remote node (using an optical splitter) which is a passive optical divider.
FIG. 1 shows a configuration of a general PON, and as shown in FIG. 1, an OLT 1 having an optical transceiver 1a for converting an electric signal and an optical signal to each other is connected with a plurality of subscriber ONTs 2 through a remote node RN, and each ONT 2 also has an optical transceiver 2a. 
In the PON structure configured above, a transmission distance between the OLT of the telephone station and the ONT of the subscriber is generally within about 20 Km, and in the case of not a large city, since a service is often not provided due to the lack of the number of subscribers according to the transmission distance limit of 20 Km, a method of extending the transmission distance by installing a plurality of telephone stations or installing a branch station has been used.
FIG. 2 shows a configuration of using a branch station to extend the transmission distance of the PON.
As shown in FIG. 2, a branch station 11 is configured within a distance (20 Km) that can be transmitted through a telephone station 10 and the corresponding branch station 11 operates as a new OLT and connected to the subscriber ONT 2 within 20 Km.
Therefore, when such a method is used, the transmission distance is doubled, but the economical efficiency is low because the cost for installing the branch station 11 and the cost for operating the branch station 11 are excessive.
That is, in the case of the telephone station 10 or the branch station 11, since an operator and a waiter need to reside and the communication data is recovered and then transmitted again, the installation cost is extremely high and the operation cost is excessively increased.
Therefore, efforts are being made to increase the transmission distance by another method. For example, although the transmission distance may be extended by increasing a signal output and lowering reception sensitivity, there is a problem that there is a limitation in increasing the output and sensitivity of an optical transceiver, the extension of the transmission distance is also behind the expectations, and the cost is excessive because the quality of the optical transceiver configured in the ONT of each subscriber needs to be increased.
Another method is a method using a relay, and methods using an optical relay of configuring an optical amplifier amplifying a transmitted optical signal itself on a line or an optical electric optical (O-E-O) method of converting a received optical signal to an electrical signal and converting the electrical signal to the optical signal again are representative.
However, since an optical amplifier that amplifies the optical signal of an optical fiber to which a broadband optical signal is transmitted as a whole is very expensive, the cost is expensive, and the optical relay is economical because the cost is relatively inexpensive. However, since a transmission packet is damaged by a delay in the converting process, there is a limitation that it is difficult to be applied at gigabit or higher.
In Korean Patent Publication No. 10-2011-0063034, there is disclosed “a relay apparatus and a relay method of a gigabit passive optical network” which converts an optical signal transmitted while using an optical relay into an electrical signal and then modulates the corresponding signal to analyze frame data, and confirms control information on an upstream burst signal, recovers and modulates the upstream burst signal transmitted according to the corresponding control signal, and then newly reconfigures the upstream burst signal to relay the recovered upstream burst signal as a continuous signal, thereby solve a delay problem generated in the optical relay. However, in this case, the frame modulation for recovering the transmitted signal and an analysis configuration for signals of the entire frame for confirming the control information on the upstream burst signal are required, and as an operation load increases, FPGA or dedicated ASIC is required to provide complex logic functionality required to configure the same function. In the case of implementing the configuration, since the economical efficiency is low and the upstream burst signal is reconfigured into a new continuous signal unlike a standard, the OLT receiving the upstream burst signal needs to be modified to correspond to the changed signal, and thus, there is a limitation in that the existing OLT cannot be used.
Accordingly, there is a growing need for an optical relay in which a stable transmission distance can be extended even while the PON components that are already configured are used themselves and the configuration cost and the operation load are low.